1. Field of the Invention
The present invention relates to illumination apparatus and more particularly, to a multiple source lighting fixture having a multiple reflector optical system.
2. Description of the Prior Art
Prior approaches to providing adjustability in the intensity of illumination from a lighting fixture have generally relied on increasing either the wattage or the size of the light source or increasing the number of light sources in a single lighting fixture. For example, Herold U.S. Pat. No. 3,927,313 discloses a surgical lighting fixture having several individual light sources evenly arranged around a central axis.
A problem with conventional multiple source lightheads however, is that they produce multiple individual light beams which, in turn, produce multiple shadows when the beams are interrupted. Efforts to reduce shadow formation have been made. Brendgord et al. U.S. Pat. No. 4,037,096 which issued on July 19, 1977, discloses a single source lighthead used with a multiple reflector optical system. The light rays are directed by means of the multiple reflectors to approach the illuminated area in an angled relationship to the axis of symmetry of the lighting apparatus, rather than parallel to the axis. Because the light rays approach objects from all angles, they tend to travel around the object, thus, reducing shadow formation on the desired area.
Applicant's co-pending application for MULTIPLE SOURCE LIGHTING FIXTURE, Ser. No. 754,704, filed July 15, 1985 also addresses the problem of reducing multiple shadows.
In some applications, for example, cardiovascular surgery, a larger pattern of illumination is preferred. Single source lightheads do not provide both high intensity and a large pattern of illumination. To achieve the desired intensity, the pattern of illumination must be limited or the wattage of the bulb increased. To achieve a large pattern, the intensity is reduced. In Europe, the trend is to couple larger surgical lights to provide a larger illumination pattern with a smaller light of greater intensity to pinpoint a critical area.
Where one lighting fixture is used for a variety of applications, those requiring high intensity and those requiring a large pattern, the lighting fixture should be adjustable to accommodate different needs. Several commercially available lighting fixtures provide some adjustability by means of altering the position of the entire lighting fixture relative to the work surface or by means of complicated light source positioning. For example, by altering the distance between the light source and the reflector in the lighting fixture, the pattern size and intensity can be varied.
There is a need for a means of adjusting the intensity and pattern of illumination in a multiple light source lighting fixture to accommodate a variety of lighting applications. There is a further need to provide such an adjusting means which is simple to use and does not require moving the entire lighting fixture or the light sources.